1. Field of the Invention
The present invention generally relates to liquid drop jet heads and ink jet recording apparatuses, and more particularly, to a liquid drop jet head used for an ink jet recording apparatus and the ink jet recording apparatus used as a picture recording apparatus or picture forming apparatus.
2. Description of the Related Art
An ink jet recording apparatus is used as a picture forming apparatus or picture recording apparatus such as a printer, facsimile, or copy machine. An ink jet head is used for the ink jet recording apparatus as a liquid drop jet head. The ink jet head includes a nozzle, a liquid room, and a pressure generating means. An ink drop is jetted out by the nozzle. The nozzle is connected to the liquid room. The liquid room is called a pressurized liquid room, pressure room, jet room, or ink channel. The ink in the liquid room is pressurized by the pressure generating means. The ink drop is jetted out from the nozzle due to the pressure in the liquid room generated by the pressure generating means.
There are several types of ink jet heads such as a piezo type, a bubble type (thermal type) or an electrostatic type. In the piezo type ink jet head, the ink drop is jetted out by deforming or displacing a vibration board forming a wall surface of the liquid room with a electric machine conversion element such as a piezoelectric element. In the bubble type ink jet head, the ink drop is jetted out by a bubble generated by boiling an ink film with an electric heat conversion element. In the static electricity type ink jet head, the ink drop is jetted out by deforming the vibration board with an electrostatic force caused by the vibration board (or an electrode united with the vibration board) forming the wall surface of the liquid room and an electrode facing the vibration board.
In a related art ink jet head, a liquid room and a common liquid room connected to the liquid room are made of photosensitive resin, resin mold, metal, glass or others. However, since the liquid room made of resin has low rigidity, cross talk is apt to occur between neighboring liquid rooms so that it is not possible to obtain a high quality picture. On the other hand, a liquid room made of metal or glass has high rigidity so that the problem regarding cross talk is small. However, since it is difficult for the liquid room made of metal or glass to be processed, it is difficult to meet a demand that the ink jet head have a high density to obtain a high quality picture.
In order to solve the above mentioned problems, for example, it is proposed to form the liquid room or the common liquid room by anisotropic-etching of a silicon substrate (silicon wafer), in Japanese Laid-Open Patent Applications No. 7-132595 and No. 7-276626. The silicon has a high rigidity and can be fine-processed by anisotropic-etching. Particularly, it is possible to form a perpendicular wall surface by using the silicon wafer of a surface direction of (110), so that the liquid room can be arranged with high density.
FIG. 1 is a plan view for explaining a configuration of the liquid room of a related art ink jet head. The liquid room structure of the related art shown in FIG. 1 is made by anisotropic-etching of the silicon substrate of the surface direction of (110). Plural liquid rooms 201, a common liquid room 202 and an ink supply opening part 203 are arranged in the liquid room structure. Each of the liquid rooms 201 has a configuration of a parallelogram on a plane level. The common liquid room 202 has a polygonal configuration consisting of plural parallelograms on a plane level. The common liquid room 202 is connected to the liquid rooms 201 by a fluid resister part (ink supply channel) not shown in FIG. 1. The ink is supplied from outside of the ink jet head to the common room 202 by the ink supply opening part 203.
When the liquid room 201 or the common liquid room 202 is formed by anisotropic-etching of the silicon substrate, the configuration of the liquid room 201 or the common liquid room 202 is formed only in a direction along a crystal direction due to anisotropy of the silicon substrate. Therefore, although the liquid rooms 201 are formed at a side of the direction along the crystal direction of the silicon substrate, the common liquid room 202 having a larger area than the liquid rooms 201 has a configuration tightly consisting of the tightly spaced plural parallelograms formed to a direction of the row of the liquid rooms 201. Therefore, as shown in FIG. 1, the common liquid room 202 has wall surface parts 202a and 202b which are along the row of the liquid rooms 201 and which have a configuration of saw teeth.
Meanwhile, a bubble often gets into the liquid room or the common liquid room in the ink jet head, when an ink tank is exchanged or due to an external vibration. Because of this, a bubble discharge method is applied as an operation for recovering reliability in an ink jet recording apparatus. In the method, the ink is absorbed from the nozzle or an outlet for the bubble, so that the bubble is removed together with the ink.
However, as described above, the wall surface of the common liquid room has the configuration of the saw teeth on a plane level. Therefore, a current speed of the ink supplied from the ink supply opening part 203 is reduced by the wall surfaces 202a and 202b of the common room 202. As a result, a bubble B adheres to a corner part of the wall surfaces 202a and 202b, the wall surfaces 202a and 202b having the configuration of saw teeth, so that the bubble B is not discharged. The bubble B may be left even if the bubble discharge method is applied as the operation for recovering reliability.
In this case, a bubble discharge may be improved by cutting the corner part of the wall surfaces 202a and 202b obliquely. However, there is a still problem in that the speed of the ink is reduced at an area remote from the ink supply opening part 203 by the wall surfaces 202a and 202b having the configuration of saw teeth during the operation the bubble discharge method. As a result, it is not possible to discharge the bubble completely.
Furthermore, during the ink jet operation, the ink is not sufficiently supplied to a liquid room remote from the ink supply opening part 203 so that bad jetting may result.
In addition, generally, a common liquid room connected to plural liquid rooms has a large opening area. Particularly, the opening area is further increased as the number of the nozzles increases for the high density and high speed recording. As a result, the strength of the ink jet head is reduced so that a yield rate is reduced due to damage of the ink jet head during assemble.
Furthermore, the common liquid room has a large opening part. Therefore, when a nozzle board is connected, the nozzle board is bent, damaged, or incorrectly-connected due to a non-uniform load while connecting, at the common liquid room.